For each gun, clamp one end of the arm onto the tripod’s mount, and the other onto the frame of the wheelchair. Adjust to position and aim however you like.

Mount an “ECU 1/2” or “ECU 3/4” box on the wheelchair and connect it to the chair’s electronics. (This is the sort of thing that a supplier or clinic would do for you, as it requires a brand-specific wheelchair programming device.)

Plug a 9-pin D-sub to 3.5mm splitter cable (like this or one of the “802-” cables show here) into one of the ports of the ECU box.

Choose two of the 3.5mm plugs (left and right, or whichever directions work best for the user while driving the chair), and plug them into the battery interrupters of the Nerf guns. (Alternatively, use a Y-adapter and connect one plug to both guns.)